Numerous surgical procedures and instruments have been developed to replace arteries that have become blocked by disease. Coronary Artery Bypass Graft (CABG) is a form of coronary bypass surgery in which a segment from the saphenous vein is harvested and used as a bypass graft. In the CABG procedure, access to the heart is obtained via a median sternotomy in which the rib cage is split longitudinally on the midline of the chest and the left and right rib cages are spread apart. More recently surgeons have begun using a cardiac procedure known as MIDCAB (Minimally Invasive Direct Coronary Artery Bypass) in which a small, left thoracotomy (incision between the ribs on the left chest) directly above the heart is used to expose the heart.
Because of the difficulty which may be encountered when harvesting the saphenous vein, some surgeons use the Internal Mammary Artery (IMA) as an alternate graft. Use of the IMA eliminates the need for a separate leg incision while reducing the number of anastomosis to one, an anastomosis is the surgical formation of a passage between two normally distinct vessels.
The IMA is located beneath the upper rib cage, requiring the surgeon to free the IMA from the surrounding tissue before allowing the free end to be anastomosed to the coronary artery. Freeing the IMA involves cutting numerous side branch arterioles, requiring prompt hemostasis to prevent bleeding. As a result, a need has been identified for an instrument that can facilitate the severance of the IMA while providing hemostatic capabilities.
In particular, in order to mobilize the IMA in an efficient and timely manner, an appropriate surgical instrument would facilitate the following procedural steps: (1) quickly score the pleura to a shallow depth on either side of the IMA along the entire length to be mobilized; (2) dissect tissue away from the IMA side branches to isolate them for coagulation and transection; (3) coagulate and transect the side branches; and (4) provide "spot" coagulation as required with a minimal of added surgeon operations if a small bleeder is encountered during soft tissue dissection. It would, therefore, be advantageous to design a surgical instrument which facilitated most or all of the steps in the foregoing procedure.
Ultrasonic instruments, including both hollow core and solid core instruments, are used for the safe and effective treatment of many medical conditions. Ultrasonic instruments, and particularly solid core ultrasonic instruments, are advantageous because they may be used to cut and/or coagulate organic tissue using energy in the form of mechanical vibrations transmitted to a surgical end effector at ultrasonic frequencies. Ultrasonic vibrations, when transmitted to organic tissue at suitable energy levels and using a suitable end effector, may be used to cut, dissect, or cauterize tissue. Ultrasonic instruments utilizing solid core technology are particularly advantageous because of the amount of ultrasonic energy that may be transmitted from the ultrasonic transducer through the waveguide to the surgical end effector. Such instruments are particularly suited for use in minimally invasive procedures, such as endoscopic or laparoscopic procedures, wherein the end effector is passed through a trocar to reach the surgical site. Ultrasonic instruments are also advantageous because tissue surrounding the cut line is coagulated as the instrument moves through the tissue.
Ultrasonic surgical instruments for cutting and coagulating tissue are known. Prior publications have illustrated the use of a variety of blades for various surgical applications, concentrating primarily on the cutting effect of the instrument. For example, see U.S. Pat. Nos. 3,888,004; 5,263,957; and 5,324,299. Other publications have focused on the coagulating effect such as, for example, U.S. Pat. Nos. 3,636,943; and 3,898,992, whereby coagulation is accelerated by the transfer of ultrasonic energy into the tissue, and by the heat generated from the vibratory movement of the blade. In addition, Recessed ultrasonic blades have has been used to facilitate the cutting of relatively loose and unsupported tissue such as fat where the recessed blade is drawn along the tissue allowing the blade to tension the tissue, enhancing the cutting action (see, for example, U.S. Pat. Nos. 5,669,922; and 5,324,299). Such blades work when the operator presses the ultrasonically vibrating blade directly against the tissue with sufficient pressure to effectively couple ultrasonic energy to the tissue.
As described previously, exists a need for an instrument which has a compact, guarded tip which could be used for controlled dissection as well as for coagulating and cutting functions in procedures such as, for example, the mobilization of the IMA in a MIDCAB procedure. While slidable sheaths have been used on ultrasonic surgical instruments in the past, for example to protect the ultrasonic blade, it would be advantageous to design a multifunction ultrasonic instrument including a slideable sheath wherein the sheath is a functional part of the instrument.
Accordingly, it would be advantageous to provide a multifunctional ultrasonic instrument which has a slideable sheath and a compact, guarded tip which could be used for controlled depth and heavy dissection as well as for cutting and coagulation functions. It would also be advantageous if the instrument included an ultrasonically isolated outer member or sheath, wherein the sheath could be moved axially to expose selected portions of the tip, resulting in a number of modes of operation.
In particular, it would be advantageous to provide a single ultrasonic surgical instrument which included a plurality of modes of operation including; 1) scoring of tissue to a controlled depth, 2) coaptive transection of vessels utilizing a clamping mechanism, 3) coagulation under tension with a blunt edge, 4) coaptive coagulation and ablation, and 5) tissue nibbling.